Brooker's merocyanine

Brooker's merocyanine (1-methyl-4-[(oxocyclohexadienylidene)ethylidene]-1,4-dihydropyridine, MOED) is an organicdye belonging to the class of merocyanines.

MOED is notable for its solvatochromic properties, meaning it changes color depending on the solvent in which it is dissolved.

As shown in the structural formula, MOED can be depicted using two resonance structures: neutral and zwitterionic. Research indicates that the zwitterionic structure is the major contributor to resonance hybrid when the compound exists in polar solvents such as water, and the neutral form when it exists in nonpolar solvents such as chloroform.